Thermochemical water splitting cycles for green hydrogen production – a comprehensive performance assessment

This article concerns with the assessment of thermochemical water-splitting cycles for green hydrogen production, using multiple key performance indicators, including conversion rate, material demand, and energy efficiency. Our analyses reveal three major limitations for most currently available materials: substantial material demand, low conversion rate (<∼10 %), and low system-level energy efficiencies (<∼20 %). Only a very small number of materials, particularly Ce-based oxides and some perovskites, e.g. (La0.8Sr0.2)(Mn0.2Fe0.2Co0.4Al0.2)O3 show a conversion rate exceeding ∼50 %. Strategies such as the increase of the reduction temperature, the enlargement of the temperature difference, the optimization of oxygen partial pressure, and the improvement of thermal management are effective in enhancing overall system performance. Our results also highlight the path-dependent heat recovery characteristics for different materials and the critical role of low oxygen partial pressure in thermochemical splitting cycles operating at medium temperatures. Optimized heat management strategies are shown to mitigate the mismatch between peak conversion rate and energy efficiency. We have also proposed a comprehensive utilization coefficient, and show that such a metric is able to evaluate thermochemical splitting cycle performance across both material and system levels.